A crankcase lubricant is oil used for general lubrication in an internal combustion engine where an oil sump is situated generally below the crankshaft of the engine and to which circulated oil returns. It is well-known to include additives in crankcase lubricants for several purposes.
There has been a need and/or requirement to reduce the level of phosphorus in crankcase lubricants in order to improve the durability of exhaust gas treatment catalysts. Reduction in phosphorus levels can, however, cause increased wear in the engine.
WO 2005/012468 A1 ('468) describes the use of a combination of dispersants to provide a proper balance of seal compatibility, corrosion protection, and antiwear performance required in modern low phosphorus-low sulphur lubricants for heavy duty diesel engines. In '468, an example of the combination of dispersants comprises products of an amine, an alcohol, or an amino alcohol, with a hydrocarbyl-substituted succinic anhydride component, when the latter component comprises: (a) 10 to 95 weight percent of a component prepared by reacting a polyisobutylene with maleic anhydride in the presence of chlorine; and (b) 5 to 90 weight percent of a component prepared by reacting a polyisobutylene with maleic anhydride in the substantial absence of chlorine.
A problem in the disclosure of '468 is that, although it discusses wear and describes the HFRR wear seal test and the High Temperature Cameron Plint Test, it does not concern itself with cam and lifter wear. Cam-plus-lifter wear is one of the parameters of the sequence IIIG test, which is an API Category SM, ILSAC Category GF-4 test carried out during high temperature conditions and which simulates high-speed service during relatively high ambient temperature conditions. Moreover, '468 does not discuss or describe piston deposits. A further problem of '468 is that it mandates the use of finite levels of chlorine which are usually regarded as undesirable for environmental reasons.